1. Field Of The Invention
This invention relates in general to magnetic flux sensing apparatus and, in particular, to a magnetic head of the type employing a thin single domain magnetic film structure as a magneto-resistive element responsive to the flux being sensed.
2. Background Relative To The Prior Art
Playback of recorded signals from a magnetic recording medium by means of a conventional magnetic head that is sensitive to flux rate-of-change is difficult for low recorded signal frequencies, and theoretically impossible for recorded DC signals, or when there is no relative speed between the recording medium and the magnetic head. Accordingly, various techniques have been proposed for sensing magnetic flux, as opposed to the rate-of-change of such flux, e.g. Hall effect, flux gate, and magneto-resistive devices, thereby to permit recording media to be used as optimally as possible.
With regard to the matter of magneto-resistive devices for sensing magnetic fields, the use of a thin single domain magnetic film for field sensing purposes is known. Representative prior art depicting the use of magneto-resistive thin-film structures can be found in the following references: U.S. Pat. Nos. 3,731,007; 3,947,889; 3,921,218; 3,945,038; 4,051,542; and 4,413,296. Typically, a thin (planar) single domain magneto-resistive film is employed to sense a magnetic field to which it is exposed by passing an electrical sense current (either AC or DC) through the film, the film magnetization vector being canted with respect to the direction of current flow. The field being sensed exerts a torque on the magnetic moment of the film, causing the resistance of the film to increase or decrease depending on the sense and magnitude of the field applied to the film. The resistance of the film is, therefore, the analog of the field strength.
There are, within the prior art, two general types of thin-film magneto-resistive heads: those in which an edge of a magneto-resistive element is adapted to ride along the surface of a magnetic recording medium to pick up magnetic signals recorded thereon; and those in which a medium-contacting structure in a magnetic yoke (or similar element) carries recorded signal flux away from a magnetic recording medium and applies such flux to a thin-film magneto-resistive element disposed in a given region of the yoke (or similar element). The invention, as will-appear below, is directed exclusively to improvements in and to the latter type thin-film magneto-resistive head, hereinafter referred to as a yoke-type magnetic head.